A typical silent chain for use in power transmission is composed of guide link rows, each comprising a pair of guide plates and a plurality of intermediate link plates disposed between the guide plates, and non-guide link rows, each comprising a plurality of inner link plates. The guide link rows and non-guide link rows are disposed alternately along the length of the chain, and the plates of the guide link rows are interleaved with the plates of the non-guide link rows and connected by connecting pins so that interconnected link rows can articulate relative to each other. Each plate has a pair of holes, one of which can be a front hole and the other of which can be a rear hole, the terms “front” and “rear” referring to the direction in which the chain ordinarily moves when in operation. A pair of connecting pins extends through each of these holes.
The shapes, dimensions, deformations, deflections, etc. of the chains of the prior art or of the invention are not represented to scale in the drawings. Instead, elements are simplified or exaggerated for the purposes of explanation. The terms “front” and “rear” are used in the description for convenient reference, referring to the usual direction of travel of the chain. However, the features described by the terms “front” and “rear” may be reversed. Therefore, the terms “first” and “second” are also used. A “first” link pin hole may, therefore, be a “front” or “rear” hole.
In the conventional chain 500 shown in FIG. 5, pairs of link plates 510 are arranged in guide link rows 501. Intermediate link plates 520 are arranged between the link plates 510 of each guide link row 501. Inner link plates 530 are arranged in non-guide link rows 502. Each plate has a pair of link pin holes.
The guide link rows and non-guide link rows are disposed alternately along the length of the chain with each plate of each row overlapping each plate of each of two adjacent rows. A pair of connecting pins for each guide link row connects the guide link rows and non-guide link rows in articulating relationship.
The first connecting pin 540 extends through the first pin holes 511 and 521 of the guide link plates 510 and the intermediate link plates 520 of each guide link row 501, and through the second pin holes 532 of the inner link plates 530 of each non-guide link row 501. The second connecting pin 540 extends and through the second pin holes 512 and 522 of the link plates 510 and the intermediate link plates 520 of each guide link row 501 and the first pin holes 531 of the inner link plates 530 of each non-guide link row 501.
The link pins 540 fit tightly into the front and rear pin holes 511 and 512, of each guide link plate 510. The link pins fit loosely into the pair of front and rear pin holes, 521, 531, 522 and 532, of each intermediate link plate 520 and each inner link plate 530. The gap between the pin and the sides of the pin holes are known.
As shown in FIG. 6, because the link pins 540 are fit tightly into the pin holes (511, 512 FIG. 5) in the guide plates 510, but loosely in the pin holes (521, 522, 531, 532 FIG. 5) of the inner link 530 and intermediate link plates 520, the link pins 540 tend to bend when tension is applied to the chain in the direction of motion F. As a result of the bending of the connecting pins, tension is applied to the intermediate link plates and inner link plates unevenly, reducing the overall tensile strength of the chain, increasing elongation of the chain due to excessive wear, and increasing noise due to repetitive deformation.
Japanese Laid-Open Patent Applications 2009-174606 and 2009-174607 address this problem by varying the diameters and pitches of the pin holes in the plates of each non-guide row with increasing distance from the guide plates. This construction allows tensile force to distribute more uniformly despite deflection of the connecting pins. Thus, wear, elongation and the likelihood of rupture are reduced.
While these chains alleviate the tension imbalance to a degree, the bend of the link pins and the warp of the guide link plates are not eliminated, and the problems of wear, elongation, heat and noise discussed above, are still present.
In addition, because the diameter and pitch of the holes of each of the inner link plates vary, each must be manufactured separately and positioned in the chain accurately. Thus, production and assembly costs are increased.
Further, because the size and pitch of the pin holes are defined based on a predetermined bend in the connecting pin, any variation in the bend of the pin, due to variation of the chain tension, results in an imbalance, reducing the overall strength of the chain.